Experimental–computational estimation of rough fracture surface contact stresses

This paper presents the preliminary results of a technique for estimating the contact stress distribution on the rough surfaces of cracks which are partially closed and loaded in shear. Phase shifted speckle interferrometric measurements of the crack face opening and sliding displacements of a crack in a four-point-bend mixed-mode fracture specimen under quasi-static cyclic loading are used as the initial data. An iterative computational process determines acceptable fits of the initial displacement data and the corresponding crack face contact stresses, which are found from a numerical model of the specimen and loading. Contact stress results are presented from one specimen at two load increments which suggest that the roughness causes an increase in the contact length compared to flat and smooth surfaces. More importantly, as the extent of sliding increases, the effective frictional resistance becomes localized and is a strong function of position along the contact. This cannot be modeled by Coulomb friction with a single value of the coefficient of friction. These are the first results of their kind ever presented for the local displacement and contact stress distributions across rough interacting fracture surfaces.